For a digital camera, a digital video and the like, a Charge Coupled Device (CCD) image sensor, a Complementary Metal Oxide Semiconductor (CMOS) image sensor and the like (hereinafter, referred to as solid-state imaging devices) are used. However, spectral characteristics of the solid-state imaging devices have high sensitivities with respect to infrared light as compared to human visibility characteristics. Hence, spectral correction by a near-infrared cut filter is performed in the digital camera, the digital video and the like.
As the near-infrared cut filter, for example, a near-infrared absorption type color glass filter such as fluorophosphate-based glass containing Cu2+ ions as a coloring component has been used. However, since the light in a near-infrared region and an ultraviolet region cannot be sufficiently cut only by the color glass filter, an optical multilayer having characteristics capable of cutting near-infrared light is used in combination at present.
The optical multilayer is required to cause no phenomenon of decreasing in transmittance (ripple) in a transmission band from 400 to 700 nm that the solid-state imaging devices requires. In the optical multilayer, a technique of suppressing the ripple has been proposed (Japanese Patent No. 4672101 and Japanese Patent Application Laid-open No. 2008-139693).